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For exceptions, permission may be sought for such use through Elsevier’s permissions site at: http://www.elsevier.com/locate/permissionusematerial From Hommel, B. Conscious and Unconscious Control of Spatial Action. In Reference Module in Neuroscience and Biobehavioral Psychology, Elsevier, 2017. ISBN 9780128093245 © 2017 Elsevier Inc. All rights reserved. Elsevier Author's personal copy Conscious and Unconscious Control of Spatial Actionq B Hommel, Leiden University, Leiden, The Netherlands Ó 2017 Elsevier Inc. All rights reserved. Introduction 1 Action Control 2 Actions and Effects 2 Will and Consciousness 3 Motor Programs and Action Plans 3 Sensorimotor Processing 4 Single-Pathway Models 4 Multiple-Pathway Models 4 Interacting Levels of Action Control 6 Role and Function of Conscious Control 7 Further Reading 8 Glossary Action effect Sensory consequences of actions Feedback Feedback control considers action-produced, (reafference), assumed to be integrated with the actions reafferent stimulation to fine-tune or stop the action, they accompany and to serve as their “mental” retrieval that is, preliminary results of an ongoing process can cues. influence earlier stages of the process in a continuous Dual-pathway models of sensorimotor processing loop. Models assuming that sensory codes are translated into Feedforward Feedforward control consists of the complete motor activity along two processing pathways, one prespecification of an action, which then runs off in subserving direct online sensorimotor transformation and a ballistic, context-insensitive fashion. another allowing for perceptual elaboration and off-line Motor program Originally a concept to refer to lists of action planning. muscle instructions, later relaxed to allow for more abstract Executive ignorance The phenomenon that voluntary representations of only the invariant properties of actions. agents have conscious access to their action goals Somatic marker A representation of the affective only but no insight into how these are translated into consequences of an action (action effects), which can be action. used as a shortcut to the action in selection processes. Introduction Any overt action carried out with the muscles, moves the body in space. This is particularly obvious if we actively navigate through our environment or for manual actions, such as grasping a cup of coffee or playing piano. But even actions that serve entirely nonspatial purposes, such as speaking to someone or singing, are controlled at lower motoric levels by targeting partic- ular spatial end configurations of one’s jaws, lips, and tongue. Nor should we forget the actions we carry out to generate percep- tual information, such as scanning a visual scene with one’seyes,turningone’sheadandearstosoundsources,and systematically exploring the texture of surfaces with one’s hand. Hence, we move our body in space all day long, and thereby change the configuration of our body parts and their relationship with the environment. At the same time, however, there is very little we know about all these changes and the ways we achieve them. Consider, for instance, if you were asked how you tie your shoes or how you ride a bike (assuming that you master these skills). Presumably, there is very little of interest you could say, simply because you know very little about the details. Most of your description will not differ much from what any other observer could see just as well (that you pick the right shoe lace with the index finger and thumb of your right hand, and so forth), which implies that you have no privileged knowledge about how you move your body in space. How is this possible, that you can move almost any limb of yours in almost any physically possible way, and yet have no idea how? This phenomenon of executive ignorance, as it is sometimes called, has been studied for more than 150 years by now and, fortunately, some progress has been made. q Change History: September 2015. B Hommel updated abstract, keywords, Biographical section, and Figures. Reference Module in Neuroscience and Biobehavioral Psychology http://dx.doi.org/10.1016/B978-0-12-809324-5.05929-0 1 Reference Module in Neuroscience and Biobehavioral Psychology, 2017, 1–8 Author's personal copy 2 Conscious and Unconscious Control of Spatial Action Action Control Human action is characterized by its voluntary nature, that is, with very few exceptions we do not respond to stimuli in an invariant, reflexive manner but carry out movements to reach a particular goal. One may ask whether this is possibly an illusion and actions are only interpreted as being goal-directed after the fact. However, the final goal actions aim at, often shapes the movement elements needed to reach it, so that actions reflect their goal right from the start. For instance, grasping an object entails a number of sequen- tial movement features, with one being the aperture of the hand adjusting to the size of the object long before the contact is made. Another example is the way people pick up an object they want to move – such as when putting a book back into a shelf – which is commonly chosen to guarantee a comfortable position of the hand at the end of the action (the end state comfort principle). These and other observations have led to the idea that voluntary actions are mediated and driven by motor programs, which are conceived as stored representations of actions that can be retrieved and used for controlling them at will, even in the absence of feedback. Numerous findings have supported this idea of a central engram of action. For instance, patients with a complete loss of kinaesthetic feedback are still able to carry out goal-directed actions with the afflicted limb, and experimentally deafferented monkeys can still grasp, walk, and jump. Other interesting observations stem from analyses of action errors. Errors sometimes anticipate later action elements and thus are actually correct action components at the wrong time – famous examples are the expressions delivered from William Archibald Spooner, such as “the queer old dean” (where he actually wanted to refer to “the dear old queen”). Less entertaining examples are everyday lapses in the order of sequential manual actions, such as when making tea or coffee, or typing errors, such as correctly doubling the wrong “leeter.” Further evidence is provided by experimental studies of actions varying in complexity, such as the number of action steps or their accuracy demands, that show that the time needed to execute an action increases with complexity. Hence, there is strong evidence that actions are commonly guided by internal representations, including the actions’ goal. Actions and Effects Combining the phenomenon of “executive ignorance” (ie, the observation that people do not have much insight into the “how” of their voluntary actions) with the assumption that voluntary actions are guided by something like motor programs poses an impor- tant question: If we have no conscious access to the contents of motor programs, how are we able to select them? One possible, philosophically very interesting answer will be considered in the next section: consciousness may not have anything to do with the selection of actions but, rather, may merely serve to make sense of or justify these actions after the fact. But there is another possibility. As ideomotor theorists in the 19th century such as Hermann Lotze and William James suggested, conscious experience may well be associated with (and perhaps even be causally effective in) the selection of the action goal, which then in one way or another takes care of the further motor programming itself. The developing infant and the novice facing a novel motor task may start by carrying out all sorts of involuntary movements, a process sometimes called “motor babbling.” The motor patterns generating these movements may be set up entirely by chance or follow genetically specified reflexes, but they should systematically produce particular sensory feedback. An automatic integration mechanism may associate the motor patterns and the perceived action effects in a bidirectional fashion. If so, the motor pattern could later be intentionally retrieved by endogenously activating an aimed-at action effect – thinking of the goal triggers the movements necessary to reach it without any conscious insight into their inner workings. Numerous studies have in fact revealed that people pick up novel effects of their movements spontaneously and continuously, thereby steadily increasing their action repertoire and the number of goals they can realize. Spontaneous acquisition has been observed in adults, children, and infants, and experiments have demonstrated that